This invention relates to a portable power operated tool, and more particularly to improvements in such a type of tool as having a cutting implement mounted at one end of an elongated tubular housing and driven by a lightweight engine connected to the other end of the tubular housing, for cutting brush, mowing grass, pruning branches or performing a number of like tasks.
In the above-mentioned type of portable power tool, several modes have heretofore been proposed, every of which, however, has considerable deficiencies in balance, safety and/or ease in manipulation during operation. For example, in use of one typical model of the conventional tool as illustrated in FIG. 19 of the accompanying drawings wherein the tool A has a handle grip 1a for the left hand which is secured to a slidable member 2 adjustably mounted on an elongated tubular housing 3 so as to extend at right angles with respect to said tubular housing 3 and a further handle grip 4a for the right hand which is axially mounted on and secured to the tubular housing 3 in place between the handle grip 1a and an engine 5, it is very difficult for the operator to hold the tool A in good balance because the engine 5 is much heavier than a cutting implement 6 which is operatively mounted to the forward end of the tubular housing 3. Therefore, when the cutting implement 6 is swung in one direction, the engine 5 is naturally swung in the opposite direction with a considerably great inertial force. In order to overcome this inertial force, the operator must handle the tool A with a physical strength at least greater than said inertial force, causing not only his fatigue but also difficulty in his quick and accurate manipulation. The latter problem is especially very important from the viewpoint of safety.
Further, supposing the cutting implement being a rotary cutter, when the rotary cutter rotating at a high speed collides with an obstacle such as a stone in the brush, the operator is occasionally subjected to so great reaction force that he can hardly hold the tool in a safe position by overcoming said reaction force imparted to him, causing thereby a great danger to someone who might be near the operator. Furthermore, as apparent from FIG. 19, the operator must hold his right elbow in an unnaturally raised position during manipulation of the tool A, it is very difficult for him to continue his performance for a long time. Further, it is almost impossible to perform a desired cutting task with maintaining the cutter 6 above the level higher than the operator's head.
FIG. 20 shows a further example of the conventional tool as disclosed in U.S. Pat. No. 3,781,991 to Stretton et al and U.S. Pat. No. 3,453,732 to Wilkin, in which the tool B is provided with a shoulder strap 7 and a U-shaped handle 8 with a pair of grips 8a which is slidably mounted on an elongated tubular housing 3. In use of the tool B, a greater part of the weight of the tool can be supported by the operator's shoulder by means of the strap 7, apparently reducing the fatigue of the operator. However, the problem of said inertial force still remains unsolved. More particularly, when the cutter 6 is swung in one direction, the engine 5 is simultaneously swung in the opposite direction with developing a considerably great inertial force, which causes difficulty not only in holding the tool B in good balance but also in manipulating the tool very quickly and smoothly, thereby inviting the fatigue of the operator. This model of the tool is especially inconvenient in cutting grass or brush on uneven ground, since the U-shaped handle 8 will not permit to change the cutting angle of the cutter 6 very quickly in accordance with the changes of the ground configuration. The reason therefor is apparent from that it is necessary to provide a sufficient distance between one of the grips 8a and the elongated tubular housing 3 in order to permit easy manipulation of the tool B. Thus, in order to change the angle of the cutter 6 by turning the tubular housing 3 about its longitudinal axis, it is inevitable to turn the grips 8a by a large angular distance about the axis of the tubular housing 8. In other words, the operator must manipulate the tool B with a somewhat exaggerated motion, and therefore it is impossible for him to change the cutting angle of the tool B very quickly. If he tries to manipulate it very quickly, he will get tired in a very short time. Further, the tool with a U-shaped handle 8 is not very convenient for performing cutting works with the tubular housing 3 directed upwardly. The difficulty in quick control of the tool B also invites the problem of the safety in operation.
FIGS. 21 and 22 illustrate further examples of the prior art devices both disclosed in Japanese Utility Model application No. 44122/1974 (Public Disclosure No. 134226/1975), wherein an arm supporting means 9c or 9d is fixedly secured to the top side of the elongated tubular housing and in front of said arm supporting means is provided a handle grip 1c or 1d, respectively. The inventor of this type of tools C and D mentions in his specification that the tools of his invention permit single hand manipulation by placing the operator's hand on or in the arm supporting means 9c or 9d. However, such type of tool C or D as having the arm supporting means 9c or 9d is not very convenient for cutting grass or brush on the sloping ground where the cutting implement 6 must take an inclined position so as to meet the inclination of the ground surface. More particularly, the arm supporting means 9c shown in FIG. 21 does not work well in performance on the sloping ground because the operator's arm easily slips out of the place, while, on the other hand, the arm supporting means 9d as shown in FIG. 22 can prevent the slipping-out of the operator's arm, but it has a deficiency that when the tool D is tilted for the cutting performance on the sloping ground, the weight of the engine 3 causes to develop the moment of rotation in the direction of an arrow P as shown in FIG. 23, resulting in that the operator must continue to overcome the moment of rotation in order to carry out the performance, thereby causing the easy and quick fatigue of the operator. Each of the tools C, D has a further deficiency that it is very difficult to maintain the tool in good balance against the moment of rotation about the axis of the tubular housing 3, because the operator's arms must always be positioned above the tubular housing 3, resulting in that it is very difficult to change the cutting angles of the cutter 6 quickly and smoothly in accordance with variable configuration of the ground where the cutting performance is carried out.
Therefore, an object of the present invention is to eliminate the above-discussed prior art deficiencies seen in manipulation of such type of portable power operated tools as having a cutting implement mounted at one end of an elongated tubular housing and driven by a lightweight engine connected to the other end of the tubular housing, for cutting brush, mowing grass, pruning branches or performing a number of like tasks.
Another object of the invention is to provide a portable power operated tool which permits safe, correct and nimble manipulation of the toll during cutting performance not only on plain grounds but also on uneven or sloping grounds.
A further object of the invention is to provide a portable power operated tool which is capable of remarkably reducing an operator's fatigue.
A still further object of the invention is to provide a portable power operated tool which can minimize the undesirable influence upon minipulation of the tool caused by inertial force inevitably developed when the tool is swung during cutting performance.
A yet further object of the invention is to provide a portable power operated tool which permits the operator to carry out cutting performance in his comfortable posture.
A still further object of the invention is to provide a portable power operated tool which has a means for fixing the operator's forearm closely to one side of the elongated tubular housing, thereby enabling the operator to manipulate the tool correctly, easily, quickly and safely.
A further object of the invention is to provide a portable power operated tool which permits the operator to continue his cutting work with a cutting implement tilted about the axis of the elongated tubular housing by a desired angle, without being effected by the moment of rotation derived from the weight of the engine and other parts of the tool.
A still further object of the invention is to provide a portable power tool which enables the operator to easily support the tool against the reaction force developed and imparted to him when the cutting implement collides with a certain obstacle, for example a stone hidden in the brush.
A yet further object of this invention is to provide a portable power operated tool which is not complicated in construction and permits manufacture and maintenance at a low cost.
Other objects, features and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter; it should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.